Hills are among the most basic sort of terrain you need for a wargames table. Here’s some nice advice on building inexpensive cardboard hills.
Modeling
Build A Cheap and Quick Wargames Table
Here’s some good advice on quickly building a relatively inexpensive wargames table.
Making A Skull Cave
Terrain Thralls has an illustrated tutorial on making an impressive Skull Cave terrain feature.
Making Wargames Terrain From Christmas Villages
I have often looked at those cheap Christmas village buildings and thought that they would be great for tabletop wargaming — if only they didn’t have those piles of molded snow and Christmas decorations. Here’s an article about converting one of those pieces.
The solution to the snow piles is a head slapper: convert them to patches of moss with foam turf.
Making Wire Trees
The DC 2150 Blog has an entry on making wire trees.